Droplet synchronization for electrostatic printing

ABSTRACT

A wire is disposed concentrically within the nozzle of a printer to define a channel for ink which issues from the nozzle along a downstream projecting end portion of the wire. An electromagnet is arranged to oscillate the wire for imparting a synchronous disturbance to ink flowing about said end portion, whereby ink droplets may be generated at a uniform frequency in a stream moving across a span in which the droplets are deflected for printingly impinging a carrier spaced downstream from the nozzle.

United States Patent 1 3,698,002 Appel [4 1 Oct. 10, 1972 4] DROPLET SYNCHRONIZATION FOR 3,329,964 7/1967 Mutschler et a1 ..346/ 140 X ELECTROSTATIC PRINTING 3,341,859 9/1967 Adams ..346/l40 [72] Inventor: Sherman P. Appel, Chicago, Ill. [73] Assignee: Teletype Corporation, Skokie, Ill. [22] Filed: Aug. 18, 1971 [21] Appl. No.: 172,793

[52] US. Cl ..346/1, 346/75 [51] Int. Cl. ..G0ld 15/18 [58] Field of Search ..346/ 140, 75, l

[56] References Cited UNITED STATES PATENTS 2,600,129 6/1952 Richards ..3l7/3 3,281,859 10/1966 Stone ..346/75 Primary Examiner-Joseph W. Hartary Attorney-J. L. Landis et al.

[ ABSTRACT A wire is disposed concentrically within the nozzle of a printer to define a channel for ink which issues from the nozzle along a downstream projecting end portion of the wire. An electromagnet is arranged to oscillate the wire for imparting a synchronous disturbance to ink flowing about said end portion, whereby ink droplets may be generated at a uniform frequency in a stream moving across a span in which the droplets are deflected for printingly impinging a carrier spaced downstream from the nozzle.

10Claims, 4 Drawing Figures DROPLET SYNCHRONIZATION FOR ELECTROSTATIC PRINTING FIELD OF THE INVENTION The present invention relates to electrostatic mass transfer. Particularly it relates to the art of printing by electrostatically deflecting ink droplets formed from a stream issued from a nozzle connected to an ink source. Specifically the invention relates to means for synchronously forming ink droplets in an electrostatic printer.

The general type of electrostatic transferring process with which the present invention is concerned is exemplified by U. S. Pat. No. 3,060,429, issued Oct. 23, 1962, on the application of C. R. Winston. That patent discloses transferring an ink mass across a span between a reservoir and an ink receiving member or carrier by electrostatically drawing the ink mass from a nozzle into a jet stream of droplets, and electrostatically moving the droplets through the span toward the carrier on which said droplets impinge for printing.

Two pair of deflection electrodes are arranged for imposing horizontal and vertical stream-deflecting potentials of variable magnitude on the droplets, 2

thereby enabling tracing of patterns with the transferred ink. This process is referred to as electrostatic jet printing.

A heretofore known development in electrostatic jet printing is disclosed in U. S. Pat. No. 3,500,436, issued Mar. 10, 1970, to R. W. Nordin. According to the development, referred to as synchronous jet printing, a mechanical alternation is applied to the ink mass by exciting a crystalline material coupled to an ink issuing nozzle for generating ink droplets at uniform frequency.

It is desirable to have alternate means for synchronously forming drops in a synchronous jet printing process.

It is the principal object of the present invention to provide such improved synchronous jet printing process and an improved synchronous jet printer.

SUMMARY OF THE INVENTION The foregoing, and other objects of the invention which will be apparent from the ensuing detailed description, are effected in an electrostatic printer adapted to print with selected droplets of an ink generated synchronously from a stream issuing from a nozzle. Therein, a wire associated with the nozzle has an end portion projecting downstream beyond the nozzle; and the wire is oscillated at a regular frequency for imparting synchronism to the droplets.

DESCRIPTION OF THE DRAWINGS In the ensuing detailed description, reference is had to the accompanying drawings in which:

FIG. I is a perspective view of a scheme of apparatus embodying the present invention;

FIG. 2 is an enlarged sectional view of the nozzle assembly;

FIG. 3 is an enlarged elevational view generally along line 33 of FIG. 2, showing an electromagnet included in said apparatus, with alternate positions of a wire being shown in dashed and solid lines; and

FIG. 4 is a sectional view of a nozzle assembly embodying a modified form of the invention.

DETAILED DESCRIPTION OF THE INVENTION Referring now to FIGS. 1 and 2 of the drawings, shown is electrostatic printing apparatus of the general type disclosed in said Winston patent. An ink source, represented by a reservoir 10, supplies ink 1 l for printing in a fluid phase to an issuing nozzle 12 having a bore 13 with which the reservoir is fiuidally connected. The nozzle is an electrical conductor to the end that it functions as an electrode. It is also preferably of high magnetic reluctance, being of brass fabrication, for example, and is part of a nozzle assembly 14 to be further described hereinafter.

The ink 11 is characterized in that its surface becomes charged from nozzle 12. The composition of the ink may be according to the disclosure of the copending application of Philip E. Kurz and Leonard A. Nash, Ser. No. 860,367, assigned to the assignee of the present application. Once charged, the ink can be drawn across a span 16 between the nozzle and a platen 18. This mass transfer is in consequence of an electrostatic field generated by applying a high potential difference between nozzle assembly 14 and said platen. A controlled volumetric flow may be provided at the noz- 5 zle by suitable fluid pumping means (not shown).

Initial acceleration and control of the ink flow downstream from nozzle 12 in an upstream part of the electrostatic field may be effected by a valving electrode 20 which is comparable to the single valving electrode disclosed in the aforementioned Winston patent. Electrode 20 is in the form of a plate which, in the illustrated embodiment, is charged with a positive d-c power supply from one pole of a battery 22. The opposite pole of said battery is connected to nozzle 12 for charging the ink.

In the interest of formation of a jet stream 23 of the ink axially of bore 13, a base plane 24, which may be the front wall of a nozzle body 25, is disposed parallel to body 25 and perpendicular to bore 13. Thereby, the equipotential surfaces of said electrostatic field would be parallel and plane were it not for the intrusion of the nozzle assembly and ink into said field. The intrustion distorts the tendency of the field to parallelism, such that a strong potential gradient is produced about the nozzle for drawing charged ink into a stream. The magnitude of the charges in the electrostatic field are selected such that stream integrity will be maintained and the stream flow 23 will be accelerated downstream axially of and away from bore 13. from In a manner heretofore known in the art, the issuing stream 23 breaks into a succession of droplets 26 which print by impinging on a receiving member or carrier 28. The carrier may be paper of sheeting thickness and is supported for movement downstream of nozzle 12 along platen l8 and according to directional arrow 29.

Electrode 20 has a central aperture 30 horizontally aligned with the nozzle 12 and coaxial with bore 13. Aperture 30 defines the path of the ink stream. Downstream of the electrode 20, ink droplets 26 can be deflected vertically and horizontally according to the disclosure in the aforementioned Winston patent. Herein, control of stream deflection results frm (a) vertical deflection potentials applied to a pair of horizontally disposed deflection electrodes 32 and 34, and (b) horizontal deflection potentials applied to a pair of vertically disposed deflection electrodes 36 and 38. The deflection electrodes are suitably disposed about and define the path of the stream downstream of the electrode 20.

Both sets of said deflection electrodes are adapted for application thereto of components of d-c potentials which are more positive than the potential present on electrode 20 to the end that the ink droplets, after passing any previous electrode, are further accelerated. Deflection signals may be superimposed on these do components for directing the ink droplets toward selected areas of platen 18 from, for example, a coded output (not shown) which forms no part of the present invention.

To produce proper droplet movement, platen 18 in turn is maintained at a potential which is more positive than the d-c potential applied to the deflection electrodes and from a suitable source of d-c potential, such as a battery 40 which is connected between electrode 20 and said platen. It is appreciated, of course, that the described effects can be achieved by reversing polarities of all voltages.

Ideally, the stream will be drawn coaxially with nozzle bore 13 and the droplets 26 are of equal diameter and will maintain uniform spacing if not deflected downstream of electrode 20. The expectancy of achieving these conditions is enhanced over the prior art in accordance with the present invention by provision of improved means for synchronous formation of the droplets.

Particularly, a horizontally extending wire or rod 42 is disposed within bore 13 coaxially with nozzle 12. The diameter of wire 42 is such that an annular channel 44 is defined between the outer periphery of the wire 42 and the inner surface of the nozzle bore 13, which channel serves as a passage for ink 11 from reservor as it flows through nozzle 12. Thereafter, the ink will move along a downstream projecting end portion 46 of the wire, from which it issues in the jet stream 23 to be managed as aforesaid in span 16.

Associated with nozzle assembly 14 are means generally designated 48 for oscillating the wire 42 at a regular frequency. This uniform mechanical alternation imparts synchronism to the droplets by causing periodic disturbances in the ink stream 23 flowing along the wire, thereby causing the droplets 26 to generate from the stream at a regular frequency, generally as depicted in FIG. 2.

In the embodiment of FIG. 1, oscillating means 48 comprises an electromagnet 50 comprised of a C- shaped core as shown in FIG. 3. In said embodiment, wire 42 is preferably a dielectric except for a magnetic segment 58 arranged in or on end portion 46. The electromagnet 50 is mounted such that its opposed polar core areas 52 and 54 are disposed symmetrically and transversely of end magnetic section 58 which projects into the air gap 56 between said opposed core areas. In the embodiment shown, segment 58 is a permanent magnet polarized such that one permanent magnetic pole faces core area 52 while the opposed permanent magnetic pole faces core area 54.

An alternating current source 60 which is connected to the coil 62 of electromagnet 50 is adapted to generate an alternating induced magnetic field such that wire end portion 46 will oscillate transversely of the stream 23 between the dashed line positions shown in FIG. 3 at the frequency of the current. This will impart a regular disturbance to the ink stream moving downstream along wire 42 in consequence of which droplets 26 will form at a uniform frequency.-

In the second embodiment of the invention of FIG. 4, oscillating means 48 comprises an electromagnet which has an oscillatable reed 72 arranged for oscillative response, in a manner known in the art, to an alternating current from source 74. In this embodiment, no permanent magnet is required in association with the wire 42 as its upstream end portion 76 is rigidly secured to reed 72 in a manner such that the wire 42 will oscillate axially as the reed oscillates.

The axial oscillation of wire 42 is also adapted to impart a disturbance to the stream such that ink flowing from the wire end portion into span 16, will break into droplets of uniform frequency equal to the frequency of the wire oscillations.

An arrangement (not shown) in which the portion of wire 42 extending through the nozzle is of magnetic material is also within the scope of the invention. However, if such material is also electrically conductive, then, appropriate adjustment may be required to avoid an adverse effect on the electrostatic gradient between the nozzle and electrode 20.

As many modifications in the described construction could be made, and as many widely different embodiments of the invention could be conceived without departing from the spirit and scope of the claims, it is intended that all matter contained in the accompanying specification shall be considered as illustrative only and not in a limiting sense.

Iclaim:

1. In a synchronous jet printing process, the steps of:

moving a stream of ink horizontally along a wire from a nozzle; issuing the stream from a downstream end portion of said wire; and

oscillating the wire to produce uniform disturbances in said stream for generating ink droplets at a uniform frequency.

2. A process according to claim I. wherein the wire is oscillated magnetornotively.

3. A process according to claim 2 wherein the direction of oscillation is axially of the wire.

4. A process according to claim 2 wherein the direction of oscillation is transversely of stream flow.

5. In electrostatic printing apparatus of the type adapted to print with selected droplets of an ink generated synchronously from a stream issued from a nozzle and in response to an electrical alternation, the improvement characterized by:

a wire associated with said nozzle and having an end portion projecting downstream beyond said nozzle; and

means for oscillating said wire at a regular frequency for imparting synchronism to said droplets.

6. A combination according to claim 5 wherein said oscillating means comprises an electromagnet.

7. A combination according to claim 6 further characterized in that said electromagnet is arranged for oscillating said wire axially of said stream.

8. A combination according to claim 6 wherein said electromagnet is arranged for oscillating the end portion of said wire transversely of said stream.

9. A combination according to claim 1 wherein said wire is disposed concentrically within said nozzle and defines a channel for ink through said nozzle for printing.

10. A combination according to claim 6 wherein said wire has a part of magnetic material associated with said electromagnet for effecting oscillations. 5

PO-IO50 (5/69) UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No Dated October 10,

SHERMAN P. APPEL Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In cIaim C), in line 1, change "1" to --5--. I

Signed and sealed this 6th day of March 1973.

(SEAL) Attest:

EDWARD M. FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents PO-I 050 (5/69) UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3, 9 Dated October 10, 1972 SHERMAN P. APPEL Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In Q aim Q, in line 1, change "1" to --5--. I

Signed and sealed this 6th day oi; March 1973 (SEAL) Attest:

EDWARD M.PLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

1. In a synchronous jet printing process, the steps of: moving a stream of ink horizontally along a wire from a nozzle; issuing the stream from a downstream end portion of said wire; and oscillating the wire to produce uniform disturbances in said stream for generating ink droplets at a uniform frequency.
 2. A process according to claim 1 wherein the wire is oscillated magnetomotively.
 3. A process according to claim 2 wherein the direction of oscillation is axially of the wire.
 4. A process according to claim 2 wherein the direction of oscillation is transversely of stream flow.
 5. In electrostatic printing apparatus of the type adapted to print with selected droplets of an ink generated synchronously from a stream issued from a nozzle and in response to an electrical alternation, the improvement characterized by: a wire associated with said nozzle and having an end portion projecting downstream beyond said nozzle; and means for oscillating said wire at a regular frequency for imparting synchronism to said droplets.
 6. A combination according to claim 5 wherein said oscillating means comprises an electromagnet.
 7. A combination according to claim 6 further characterized in that said electromagnet is arranged for oscillating said wire axially of said stream.
 8. A combination according to claim 6 wherein said electromagnet is arranged for oscillating the end portion of said wire transversely of said stream.
 9. A combination according to claim 1 wherein said wire is disposed concentrically within said nozzle and defines a channel for ink through said nozzle for printing.
 10. A combination according to claim 6 wherein said wire has a part of magnetic material associated with said electromagnet for effecting oscillations. 